Tracking apparatus for parabolic reflectors

ABSTRACT

A parabolic reflector having support structure, mounted upon a rotatable track, for supporting a parabolic dish framework to which is mounted one or more support panels to which, in turn, are pivotally mounted a plurality of reflectors for focusing rays on a linear collector. The support panels include a plurality of concave recesses operable to receive bowl-shaped reflectors provided with polygonal rims so that the sides of adjacent reflectors will be in registry with one another. The support panels are provided with bolts, outwardly extending from the base of each recess, the bolts being received in slotted apertures in each reflector bowl for pivoting and fastening the reflector in a pre-selected position for focusing solar rays upon the collector. The collector includes a heat exchange media operable to conduct heat at extremely high temperatures for production of steam. A novel tracking system is also provided.

This application is a division of an application filed Nov. 7, 1984,Ser. No. 668,898 entitled "Parabolic Reflector".

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to parabolic reflectors and moreparticularly to support structures, reflectors, tracking systems, andcollectors therefore.

2. Description of the Prior Art

Many parabolic reflectors have been devised to focus solar rays on apoint, at which a collector is placed, as typified by the D. E. Woodpatents, numbered U.S. Pat. Nos. 4,171,876; 4,295,709; and 4,372,772,and the Osborn patent numbered U.S. Pat. No. 4,335,578. Where rays arefocused on a point, rather than a line, greater tolerance is allowed formis-alignment of reflectors. Where solar rays are focused on a line,i.e., on a linear collector, as typified by U.S. Pat. No. 4,407,129issued to B. W. Johnson, focusing becomes more critical. Mirrored glasshas been found to be the best reflector for solar rays, but large glasssections are prohibitively expensive. It is also highly desirable thatthe glass be curved to provide higher operating temperatures because ofsuperior focus. Attempts have been made in the prior art to forciblycurve a plane sheet of glass, but such curvature is inadequate anddistorted; extensive breakage may occur, and panes under such force arenot individually focusable.

SUMMARY OF THE INVENTION

The present invention overcomes problems of focusing efficiency found inthe prior art by providing a parabolic reflector including a noveltracking system supporting dish framework which, in turn, supportsinsulative panels provided with a plurality of recesses with attachmentmeans for pivotal attachment of bowl-shaped reflectors. The reflectorsare individually adjustable to focus solar rays upon a linear collectorfor flashing water to steam for power production and for purification ofwater. A more detailed description of the invention may be found in theappended claims.

It is therefore a principal object of the present invention to provide aparabolic reflector having a plurality of separately focusable curvedglass reflectors for focusing solar rays on a linear collector.

More specifically, it is an object of the present invention to provide asupport panel having a plurality of concave recesses, each recessadapted to receive and hold a concave reflector in a pre-selectedfocusing position.

Even more specifically, it is an object of the present invention toprovide pivotal reflectors having polygonal rims for registry with rimsof adjacent reflectors for superior efficiency.

It is also an object of the present invention to provide a linearcollector operable to receive solar rays thus focused and to transferheat from such rays to flash water to steam.

Another object of the present invention is to provide a tracking systemhaving high stability and a minimum of maintenance.

Additional objects and advantages will become apparent and a morethorough and comprehensive understanding may be had from theaccompanying drawings forming a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a parabolic reflector made in accordancewith the present invention, showing individual reflector members inpart.

FIG. 2 is a plan view of one of the reflectors of the present invention.

FIG. 3 is a sectional view taken along lines 3--3 of FIG. 2.

FIG. 4 is a perspective view of a reflector showing a hexagonal rim andthe concave reflecting surface.

FIG. 5 is a perspective view in partial section showing the framework,support panel composition, and reflectors mounted thereon.

FIG. 6 is a sectional view taken along lines 6--6 of FIG. 5.

FIG. 7 is a rear view of a horizontal framework of the presentinvention.

FIG. 8 is a perspective view in partial section of one embodiment of thelinear collector of the present invention.

FIG. 9 is a plan view of the track of the present invention.

FIG. 10 is a sectional view taken along lines 10--10 of FIG. 9.

FIG. 11 is a perspective view of one embodiment of the present inventionutilizing a horizontal linear collector.

FIG. 12 is a plan view of an octagonal framework showing one panel inplace having some octagonal reflectors thereon, and an octagonalcollector.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and, more particularly, to FIG. 1, anembodiment to be preferred of a parabolic dish reflector 10, madeaccording to the present invention is disclosed. Parabolic reflector 10includes a support structure 20 holding a parabolic dish framework 30which underlies one or more support panels 40, as shown in FIGS. 5 and6, upon which individual reflectors 50 are attached. Reflectors 50 focussolar rays upon a centrally located linear collector 70 verticallymounted at the longitudinal axis of the dish upon framework 30 and shownin outline on FIG. 1. Tracking apparatus, designated generally by thenumeral 90 rotatably carries support structure 20.

The tracking apparatus, shown to advantage in FIGS. 9 and 10, includes acircular and tubular track 95 equidistantly spaced about a vertical axisabout which the reflector support structure 20 is rotated. Track 95 iscircular in cross section and provided with a continuous slot 96 locatedon the inner curvature of the track. The track may be manufactured insections for convenience in shipping as well as maintenance. The trackis mounted to a solid foundation by a suitable number of brackets 91,shown in FIG. 1. Located in the enclosure defined by the tubular track95 are a plurality of wheels 97, preferably four, rotatably mounted uponaxles 99 by means of wheel bearings 98. Axles 99 extend laterally inwardthrough slot 96 where they supportingly engage and carry supportstructure 20, as shown in FIG. 1. Two of the wheels are powered by 12volt D.C. motors, not shown, controlled by photo-optic circuitry,allowing the reflector dish to track the sun as necessary to receiveoptimum amounts of solar rays. The track contacting surface 92 of eachof the wheels 97 is substantially identical in shape with the innersurface 93 of track 95 for mating engagement therewith and the diameterof each wheel is only slightly smaller than the inside diameter of thetubular track, maximizing surface contact between wheel and track, yetproviding for close tolerance between the top of the wheel and theinside surface of the track for stabilization and to prevent vibration.The track may be composed of any suitable material, such as steel oraluminum, and the wheels are preferably composed of rubber, plastic, orother composition having suitable load-bearing characteristics. Thetracking apparatus is substantially maintenance-free in that the tubulartrack is extremely efficient at keeping out foreign material such assand and water. A flexible cover 94 of rubber or plastic affixed to thetrack just above the slot 96 may be provided to cover the slot at alllocations except at the position of the axles to further keep the trackfree of foreign objects. The flexible cover simply rides over the axlesand drops in place on either side as the axles pass.

Support structure 20 includes two vertical supports 22 upon which dishframework 30 is pivoted. Framework 30, in the preferred embodiment iseither hexagonal or octagonal in shape, defining solar banks, andconforming to the shape of linear collector 70 and to the individualreflectors 50 indirectly carried thereupon. The framework, in theembodiment shown in FIG. 7 includes six radial support trusses 33radially extending in a selected arc from a central support ring 35,shown in FIG. 8. Referring now to FIG. 12, framework 30' is shown in anoctagonal form. The octagonal form is used to accomodate individualreflectors 50' which define an octagonal rim. In such case, a linearcollector 70', octagonal in cross section is utilized for the focusingof each bank of reflectors located between each of the support trusses33'.

Referring once again to FIG. 7, mounted laterally between adjacentradial support trusses 33 are a suitable number of lateral supportstruts 37, providing a mounted surface for support panels 40. Bothtrusses and struts are preferably constructed of aluminum because ofweight considerations.

Referring now to FIGS. 5 and 6, support panels 40 may be seen toadvantage. Each of the support panels is substantially trapezoidal inshape, extending in width to the radial trusses and extending in depthto the lateral supports. While the support panels may be attached totrusses and struts by any conventional means, it is preferred that eachpanel 40 be provided with aluminum framing 41, which may be eithertubular or L-shaped, as shown. Framing 41 includes in the embodiment andshown a vertical portion 42 about the periphery of the panel and a baseportion 43 by which the panel is mounted to the trusses and struts bybolts, welding or otherwise.

Each panel 40 includes a top surface 44 and a bottom surface 46 whichare substantially parallel to one another. Top surface 44 defines aplurality of recesses 45 for receiving reflectors 50. Recesses 45 areconcave in shape, matching the curvature of the bottom surface of thereflectors 50, and terminating in a circular upper rim planar with uppersurface 44.

Each recess is provided with means, designated generally by the numeral80, for attachment of reflectors 50. In the preferred embodiment,attachment means 80 include a bolt 82 upwardly and outwardly extendingfrom the base of each recess 45, as shown in FIG. 6. The bolt extendsthrough an elongated slot 56 in the reflector 50 with the head of thebolt engaging the top surface of the reflector to hold the reflector ina pre-selected position as will hereinafter be described. Each bolt isthreaded only a selected distance along the shaft so that engagement bynut 84 is restricted to prevent overtightening of the nut with resultantdamage to the fragile reflector. Both nuts and bolts, along with anywashers which may be used, are preferably constructed of nylon, becauseof the flexibility required. While nut and bolt assemblies have beendescribed, it is obvious that pins provided with clamps as fasteners orother equivalent fastening means may similarly be used.

Each panel 40 includes a body portion 47 constructed of rigid foaminsulation, preferably polyurethane because of weight and insulativequalities. Adhering to the upper surface of the body portion is a vinylcoating 48 for weather protection and adhering to the bottom surface ofthe body portion is a fiberglass backing 49 giving added protectivesupport.

Now referring to FIGS. 2, 3 and 4, reflector members 50 may be seen.Reflector members 50 are each formed in bowl-shaped configuration havingupper concave reflecting surface 51 for focusing solar rays upon acollector and a bottom surface conforming substantially with the uppersurface of recesses 45 for reception therein. Each of the reflectorsmembers 50 terminates in a rim lying in a single plane and defining apolygon and preferably a hexagon as shown in FIGS. 2,3, and 4, or anoctagon as shown in FIG. 12. It is important to note that the shape ofthe reflector rims dictate the shape of the entire reflector dish andthe shape of the collector as aforementioned. The polygonal rims of thereflector bowls permit close registry between rim sides of adjacentreflectors, as shown in FIG. 5, for superior efficiency in reflection.

Each reflector is molded of glass or pressed and shaped of metal, andsilvered or polished to produce a concave mirror. Each reflector alsodefines an elongated slot 56 intersecting the vertical longitudinal axisof the reflector. Slot 56 is operable to receive bolt 82 of attachmentmeans 80 with either the head of the bolt or a nylon washer 87 engagingtop surface 51 of the reflector. Each reflector 50 is pivotal withineach recess 45 and is held in a selected tilted position by tighteningnut 84 thereby bringing the washer or the head of the bolt into contactwith the reflector for proper focus upon collector 70.

Linear collector 70, shown in FIG. 8, is vertically mounted at thecenter of dish framework 30 to ring 35. The collector may also bemounted horizontally, as shown in FIG. 11, the collector beingdesignated by the numeral 70'. Such positioning may be desirable where afull reflecting dish is not required or not suitable. A framework 30'holds support panels 40', which, in turn, supports reflectors 50', eachstructural element being equivalent to the structures of like numbers inthe embodiments previously mentioned. Referring again to FIG. 8, it willbe seen that collector 70 includes a housing designated generally by thenumeral 72. Housing 72 includes an elongated tubular outer shell 73 anda pair of end members 74, only a portion of one such member being shown,to define an enclosure 75. In the preferred embodiment, as shown in thefigure, an inner shell 77, substantially coaxial with the outer shell isalso provided, the inner shell sealingly engaging the end members todefine enclosure 75 therebetween. Mounted within the enclosure andbetween the shells is a helical coil 79 having a water inlet port 76 anda steam outlet port 78. A heat transfer media 100, preferably in theform of a fluid, serves to transfer the heat between outer shell 73 andcoil 79.

While media of varying types may be used, it is preferred that a heattransfer fluid bearing the trademark "DOWTHERM LF" be used because ofits low freeze point, low viscosity, and stability. A pump, not shown,may be used to circulate the media. The outer surface of outer shell 73bears the same shape in cross section as the rim of each reflector 50and has sides equal to the number of banks of support panels containedin the dish framework 30 as previously indicated. Where hexagonal rimmedreflectors 50 are used, framework 30 includes six banks of supportpanels 40 and therefore the cross sectional shape of outer shell 73 ofreflector 70 is also hexagonal, as shown. The planar sides of thecollector result in highly efficient absorption of solar rays focusedthereupon by reflectors 50, as compared to collectors having a curvedouter surface. The planar surface of the outer shell enables eachreflector contained within each bank to focus thereupon. Where octagonalrimmed reflectors are used, then framework 30' is octagonal in shape,and a collector having an outer shell, octagonal in cross section, istherefore used. The outer surface of the collector is either anodized orcoated with a highly absorbent agent for proper heat transference.

Having thus described in detail a preferred selection of embodiments ofthe present invention, it is to be appreciated and will be apparent tothose skilled in the art that many physical changes could be made in theapparatus without altering the inventive concepts and principlesembodied therein. The present embodiments are therefore to be consideredin all respects as illustrative and not restrictive, the scope of theinvention being indicated by the appended claims rather than by theforegoing description, and all changes which come within the meaning andrange of equivalency of the claims are therefore to be embraced therein.

I claim:
 1. Tracking apparatus for a parabolic reflector rotatable abouta vertical axis, said tracking apparatus comprising:A tubular track,circular in cross section and provided with a lateral slot; and aplurality of wheel-axle assemblies supporting said reflector, the wheelsof each of said assemblies contained within said tubular track, eachwheel rotatably mounted on an axle extending laterally through the slotof said track, and each axle in supporting engagement with saidreflector.
 2. The apparatus as described in claim 1 wherein the trackcontacting surface of each wheel of each of said assemblies issubstantially identical in shape to the inner surface of said track, formating engagement therewith.
 3. The apparatus as described in claim 2wherein the outside diameter of each wheel of each assembly is slightlyless than the inside diameter of said tubular track.
 4. The apparatus asdescribed in claim 1 wherein said track is circular in shape, eachrespective portion of said track being equidistant from said verticalaxis; wherein said slot is located on the inner curvature of said track;and wherein the axles of each of said assemblies are radially andinwardly extending.
 5. The apparatus as described in claim 1 furthercomprising a flexible member for covering the slot of said track.